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Carbon monoxide (CO) is a leading cause of poisoning morbidity and mortality in the United States. It is formed during the incomplete combustion of virtually any carbon-containing compound. Because it is an odorless, colorless, and tasteless gas, it is remarkably difficult to detect in the environment even when present at high ambient concentrations. The clinical findings are protean, making diagnosis difficult, and even objective data, such as elevated carboxyhemoglobin (COHb) concentrations, are not highly prognostic unless at one of the extremes. Hyperbaric oxygen (HBO) therapy, if practical to perform, remains the treatment of choice. However, the necessity for HBO therapy remains controversial, in large part related to the controversy over the incidence and significance of the long-term clinical effects of CO exposure.

Based on U.S. national death certificate data, there were 439 annual deaths from unintentional non-fire exposure to CO from 1999 to 2004.20,107 The groups with the highest risk were male gender and elderly age, possibly because of occupational exposure and inability to discern CO symptoms, respectively. CO-related mortality remained essentially unchanged in 2002 despite increased CO detector use.21,22,23 In that time period, 2001 to 2003, there were 15,200 patients treated annually in emergency departments (EDs) for nonfatal, unintentional, non—fire-related CO exposure. More than half of these cases (64%) occurred in homes with faulty furnaces, usually in the fall or winter months. Despite increased awareness for CO poisoning, in 2004 to 2006, there were still an average of 20,636 nonfatal, unintentional, non—fire-related CO exposures treated annually in the United States.22 More than 40% of cases occurred in the winter, with almost 75% occurring in residences. However, exclusion of intentional and fire-related cases severely underestimates the extent of the problem. Based on firsthand hospital data, a minimum of 50,000 CO cases present to U.S. EDs each year.67

The more significant problem with CO poisoning may be the morbidity rather than mortality. The most serious complication is persistent or delayed neurologic or neurocognitive sequelae, which occurs in up to 50% of patients with symptomatic acute poisonings.58,128,171 To date, there is still no completely reliable method of predicting who will have a poor outcome, suggesting that the threshold for HBO therapy for CO poisoning should be appropriately low.

Potential sources of CO abound in our society, often resulting in unintentional poisoning22 (Table 125–1). Although CO is found naturally in the body as a byproduct of hemoglobin degradation by heme oxygenase found in the liver and spleen,32 it is readily available for inhalation from the incomplete combustion of virtually any carbonaceous fuel. Alternatively, absorption—dermal, ingestion, or inhalation—of methylene chloride may result in CO toxicity after hepatic metabolism112 (see Chap. 106). Despite catalytic converters and other emission controls, more than 50% of unintentional CO deaths are still caused by motor vehicle exhaust.31,107 Occupants of motor vehicles are not the only victims ...